Method of transparentizing paper



Patented Aug. 28, 1945 METHOD OF TRAN SPARENTIZIN G PAPER Julius G.Little, Wilmington, Del., asslgnor to Hercules Powder Company,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationSeptember 25, 1942, Serial No. 459,716

1 Claim. (or. 117-158) This inventionrelates to transparentized paperand the method for its production. More particularly, it is concernedwith an improved transparentized paper containing a hydrogenated rosinester and method for its production.

There aremanyknown methods of transparentizing paper. Each method,however, possesses inherent disadvantages which have not been overcome.For example, papers transparentlzed with vegetable and mineral oils andsizes alone or with combinations of these ingredients are characterizedby poor ink receptivity, Poor pencil erasive qualities, possess a greasyfeel, and have a tendency to yellow and acquire'a disagreeable odor overextended aging periods. Papers transparentized with synthetic resins ofthe oil modifled alkyd type also possess a disagreeable odor anddiscolor 'on aging.

Now, in accordance with this invention, a transparentized paper may beprepared by impregnating the paper with a glycol ester of hydrogenatedrosin. The transparentized paper thus obtained is characterized byexcellent transparency, non-yellowing on age, goodpencil and inkreceptivity, lackrof odor, and stability of properties of stiffness dueto resistance to oxidation.

Having now indicated in a general way, the nature and purpose of myinvention, the following examples are offered to give specificillustrations of the practice of the invention and the advantages to beobtained by their use thereof and are not to be construed as limitingthe same. In the examples, the ingredients are given in parts by weightunless otherwise indicated.

Example 1 A triethylene glycol ester of hydrogenated rosin, prepared bymixing 100 parts of hydrogenated rosin with 27 parts of triethyleneglycol in a vessel equipped with a steam condenser and car bcn dioxideinlet and heating to a temperature of 280 C. until the acid number ofthe ester thus formed had decreased to below 15, was dissolved 4 Example2 To 100 parts 01 the glycerol ester of hydrogenated rosin having acolor of 25 Amber, a melting point of 85 C.', and an acid number of I,prepared by reacting 100 parts hydrogenated rosin with 11 partsglycerine at a temperature of 285 C., in apparatus described in Example1, were added 100 parts of triethylene glycol ester of hydrogenatedrosin and thewhole dissolved into 100% solids. Rag stock (13 lbs/ream)'was transparentized with this resin by immersing the paper in the resinsolution, removing excess sol- .vent by-means of. squeeze rolls andallowing the paper to air dry. The transparentized paper thus producedwas equal in transparency to- Example 1 (transparency index of 54.0%)but possessed 15 increased stiffness and snap.

Example 3 The hexaethylene glycol ester of hydrogenated rosin, preparedby the same procedure used in Example 1 using100 parts of hydrogenatedrosin squeeze rolls. The transparentized paper pas-- 'sessed atransparency index of 50%.

In the examples, the transparency'is eq al to 100 units less thecontrast ratio; as measured by a General Electric Spectrophotometer. The

contrast ratio may be defined as the ratio of theSpectrophotometerreflectance at550 millimicrons using a blackbackgroundto the Spectrophotometer reflectance at 550 millimicrons using a whitebackground. The lower the "contrast ratio, the higher the transparency.

The glycol esters of hydrogenated rosin which may be utilized in thisinvention, in addition to triethylene glycol and hexaethylene glycol,include such as ethylene glycol, propylene glycol,

40 diethylene glycol, trimethylene glycol, tetraethylene glycol,pentaethylene glycol, hepta ethylene glycol, octaethylene glycol,nonaethylene glycol, decaethylene glycol, etc. However, it may be founddesirable to modify these liquid glycol 5 esters of hydrogenated rosinwith hard brittle esters of hydrogenated rosin such as the glycerylester, the pentaerythritol ester, and the sorbital ester of hydrogenatedrosin and the like.

The glycol esters of hydrogenated rosin which are employed may be madein any known manner whereby the rosin nucleus thereof has -lts doublebonds saturated with hydrogen, for example, by hydrogenating a glycolester of ordinary rosin in such manner as to partially or completelysaturate the double bonds of the rosin nucleus,

or by esterifying a glycol with previously hydrogenated rosin, theproduct of either process having virtually identical properties.

Where it is desired to prepare the glycol esters by hydrogenation of thepreviously prepared ester of rosin, this may be accomplished by treatingthe ester in molten form or in solution in a volatile organic solventwith hydrogen in the presence of a hydrogenation catalyst such as thenoble metal catalysts as platinum, iridium, ruthenium, platinum, osmium,etc.; the base metal catalyst as nickel, nickel-aluminum,nickel-silicon, etc.; also the copper chromate type catalyst. Thehydrogenated rosin ester may be saturated from about 25 to 100% of thetheoretical saturation. A preferred product is one having about 55% toabout 75% of theoretical saturation.

If it is preferred to prepare the glycol esters by esteriflcation ofhydrogenated rosin, this may be accomplished by esterifying a glycolwith hydrogenated rosin by any of the various known metheds. Thehydrogenation of the rosin may be accomplished by treatment of the rosinin molten form or in solution in a volatile organic solvent withhydrogen in the presence of a hydrogenation catalyst. The hydrogenationcatalysts indicated may be carried out in any equipment where means areprovided for immersing the paper in the resin solution and removal ofthe excess solvent with squeeze rolls for evaporating the solvent.However, any other type equipment suitable for impregnating the paperwith a solvent an aqueous emulsion of a glycol ester of hydrogenatedrosin ester. It has been found that liquid rosin ester may be easilyemulsified with water using emulsifying agents such as triethanol byimmersion in an aqueous dispersion of the hyas suitable forhydrogenation of the glycol esters of rosin are equally operablefor thehydrogenation of the rosin. The hydrogenated rosin may be saturated fromabout 25 to 100% of the theoretical saturation. A preferred product isone having about 55% to about 15% of the theoretical saturation.

In the practice oi this invention, paper may be transparentized by theimpregnation of paper stock with the glycol ester of hydrogenated rosinin a solvent solution, as a hot melt, or as an aqueous dispersion. If itis desired to transparentize paper by the use of solutions of the estersof hydrogenated rosin solvents such as benzene, carbon tetrachloride,ethyl acetate, acetone and the like may be used. When paper istransparentized by the use of a solvent solution of hydrogenated rosinesters, the concentration will depend uponthe typ paper which is to betransparentized but in general, solutions containing about 15 to about50% of hydrogenated rosin ester will be found satisfactory. If desired,however, other concentrations may be used.

The impregnation of the paper with the solvent solution of a glycolester: of hydrogenated rosin drogenated rosin ester must be dried atelevated temperature to. induce. coalescence of the resin which isdeposited in a discontinuous him and also to induce impregnation of thefiber by reducing the viscosity of the ester. I

Paper transparentized by the process of this invention is characterizedby excellent transparenc little tendency for the resin to migrate fromthe flber to the surface of the paper, good pencil and ink receptivity,good pencil erasive qualities, non-yellowing on aging, stability ofproperties of stillness due to resistance to oxidation and lack of odor.There thus has been provided by the process of this invention theimproved transperentized paper in which superior qualities oftransparency have been attained and in which the disadvantages wellknown to the art have been eliminated. i

What I claim and desire to protect by Letters Patent is: t

A method of 'transparentizing normally substantially opaque,unpigmented'fibrous, porous paper, which consists in impregnating saidpaper with a composition consisting of a 37.5% solution of a triethyleneglycol ester of hydrogenatedrosin in ethyl acetate, removing excesssolution and drying the impregnated paper.

